Effect of different heat input on the microstructure and mechanical properties of laser cladding repaired 300M steel

Laser cladding repair technology is valued for its ability to repair of damaged parts with high performance. However, there are so many parameters affect the repair quality that it takes a lot of work to determine the optimal parameters. In this article, a variety of parameters were combined as dimensionless heat input (Q∗), and the effect of Q∗ on the microstructure and mechanical properties of 300M steel repaired samples were studied. Results showed that with the increase of Q∗, microstructure of heat affected zone transformed from tempered martensite to tempered martensite and low bainite. The microstructure of the repaired zone transformed from untempered martensite to untempered martensite and a small amount of retained austenite. With increasing of Q∗, residence time above the austenitizing temperature was extended, and more uniform microstructure were obtained in the repaired zone. What's more, at Q∗ = 5.1, the repair efficiency increases twice than Q∗ = 1. The tensile strength of the repaired samples reached 1017.6 MPa and the elongation reached 6.9%, which were far lower than that of forged samples. The heat treatment was carried out on the repaired parts, which eliminated the microstructure difference due to different Q∗. Compared with the repaired samples without heat treatment, the tensile strength increased by 75% to 1783.8 MPa and the elongation increased by 86% to 10.4%.